- 1 tablespoon butter
- 1 cup whole or 2 percent milk or cream or half-and-half
- 3/4 teaspoon salt
- 1/8 teaspoon freshly ground pepper
- Pinch ancho chile powder
- Pinch nutmeg
- 1 pound Yukon Gold potatoes , peeled and sliced into 1/2-inch-thick rounds
- 1 pound sweet potatoes , peeled and sliced into 1/2-inch-thick rounds
- 3 tablespoons whole grain mustard
- 1 cup shredded Gruyere
In a large saucepan, combine milk, salt, pepper, chile powder, and nutmeg. Heat to boiling over a medium-high flame. Add potatoes and return to a boil; simmer a few minutes until mixture thickens slightly. Remove pan from heat; stir in mustard.
With a slotted spoon, transfer half the potatoes to gratin dish; place in an even layer. Sprinkle with 1/2 cup Gruyère. Top with remaining potatoes; pour milk mixture over potatoes and sprinkle with remaining 1/2 cup Gruyère. Bake 40 minutes, until potatoes are tender and top is golden.